Method of plating copper on aluminum

ABSTRACT

Copper is electroplated directly onto aluminum by immersing an aluminum workpiece in an aqueous alkaline plating bath containing a divalent copper salt and an amine capable of complexing the copper, and passing an electric current through the plating bath using the workpiece as the cathode. The deposits which are obtained are strongly adherent and the method avoids the need for complicated mechanical or chemical pretreatment of the workpiece.

United States Patent Bharucha et al.

[451 Nov. 27, 1973 METHOD OF PLATING COPPER ON ALUMINUM Inventors:

Assignee:

Filed:

Appl. No.:

Nanabhai Rustomji Bharucha, Chomedey-Laval, Quebec; Mohammad Barakat Ilahi Janina, Pointe Claire, Quebec, both of Canada Canada Wire and Cable Limited, Toronto, Ontario, Canada Sept. 25, 1970 Foreign Application Priority Data May 25, 1970 Canada 83,600

US. Cl. 204/33, 204/52 R Int. Cl. C23b 5/18, C23b 5/48 Field of Search 204/52 R, 52 US,

204/52 1C, 52 IR, 52 E, 33

References Cited UNITED STATES PATENTS McConnell 204/33 3,161,575 12/1964 Wells et a1. 204/52 R 3,280,736 10/1966 Schafler et al.... 204/41 X 2,766,195 10/1956 Combs et al 204/23 2,872,346 2/1959 Miller 204/38 B FOREIGN PATENTS OR APPLICATIONS 822,628 10/1959 Great Britain 204/52 R 116,447 7/1961 U.S.S.R 204/52 R Primary Examiner-F. C. Edmundson Att0rney.1ames E. Armstrong and Ronald S. Cornell 5 7] ABSTRACT 25 Claims, No Drawings 1 METHOD OF PLATING COPPER ON ALUMINUM The present invention relates to a method of electroplating copper onto aluminum.

The electroplating of copper directly on to aluminum has hitherto been regarded as difficult or refractory and known commercial methods of plating aluminum with copper have generally involved complicated, and hence costly, mechanical or chemical pretreatments of the aluminum. One such pretreatment involves the removal of the protective surface oxide coating of the aluminum and its replacement with a strike, or layer, of a suitable metal, for example zinc. To simplify the electroplating procedure by eliminating such pretreatments clearly would materially reduce the cost of production of aluminum articles electroplated with copper.

It is an object of the present invention to provide a method of electroplating copper directly on to aluminum without the need to resort to the deposition of any intermediate layer of a metal such as zinc.

The invention accordingly provides a method of electroplating copper directly onto aluminum which comprises immersing an aluminum workpiece in an aqueous alkaline plating bath which has a'pI-l of from 8.5 to 13 and which comprises from to 450 grams per litre of a salt of divalent copper and from 5 to 450 grams per litre of, as complexing agent, A mixture of a primary, secondary or tertiary amine with ammonium hydroxide, said mixture being capable of forming a complex ion with divalent copper, andpassing an electric current through said bath between said workpiece as cathode and an anode.

It should be understood that the aluminum workpiecewhich is electroplated in accordance with the invention may be of pure aluminum metal or may be of commercial aluminum containing its usual manufacturing impurities or may be an aluminum alloy.

The plating bath which is used in the method of the present invention is alkaline having a pH of from 8.5 to 13. Preferred pH values are in the range 9.5 to 10.5 (as measured by a glass electrode pH metre) and the optimum pH varies with the concentrations as well as with the nature of the various ingredients of the plating bath. The pH may be adjusted to the most suitable value within the given range for a particular operation by using appropriate amounts of the ammonium hydroxide.

The use of an alkaline plating bath in accordance with the invention in which the copper ions are complexed by the amine ammonium hydroxide complexing agent means that chemical deposition of the copper is prevented and the passage of electric current through the bath produces a coating of electroplated copper at thickness which may range as high as about 5 mils (about 125 microns). Since, however the degree of adhesion of the deposit of copper tends to fall off with an increase in thickness clearly there is no advantage in providing too thick a deposit, especially as thicknesses of up to about 1 mil, and preferably up to about 0.5 mil, are generally quite adequate for most practical pur- P The aqueous plating bath which is used should comprise a divalent copper salt. The nature of h salt i r atively unimportant but should be such h pr ions are produced when the salt is dissolved in water. Suitable salts include copper nitrate, which is preferred, copper sulfate, copper acetate and copper chloride- The amount of divalent copper salt can vary between wide limits depending, in part, upon the salt used and upon the other plating conditions. In general suitable amounts are from 5 to 450 grams per litre with amounts of from 50, especially 100, to 200 grams per litre being preferred.

The other essential ingredient of the aqueous plating bath is the mixture of amine with ammonium hydroxide which acts as a complexing agent for the cupric ions in solution. A wide variety of amines is known to be capable of complexing copper in solution including aliphatic primary, secondary and tertiary amines, forexample acyclic lower alkyl amines, such as ethylamine, diethylamine, and triethylamine, and substituted derivatives thereof including the alkanolamines, such as triethanolamine, and polyarnines, such as ethylenediamine, diethylenetriamine and tetraethylene pentamine; cycloaliphatic amines such as hexamethylenetetrarnine and triethylenetetramine; and aromatic amines such as pyridine and derivatives thereof. Preferably the amine contains at least two nitrogen atoms and is capable of forming a chelate with divalent copper. It has been found that such amines, for example ethylene diamine, diethylene triamine and tetraethylene pentamine, together with ammonium hydroxide providethe right complexing behaviour consistent with ease of deposition of the copper on the workpiece. The amount of the amine-ammonium hydroxide complexing agent present in the plating bath should be atleast sufficient to complex the cupric ions provided by thecopper salt. Thus the amount will depend upon the-amount of copper salt and ammonium hydroxide and upon the type and amount of amine used.

Ammonium hydroxide is generally used in the form of a commercial 30 percent solution although other concentrations can be employed. It can also be formed in situ by introducing ammonia into the bath. The amount of ammonium hydroxide with reference to the amine can varyto a great extentbut generally will be such as to produce the desiredcomplexing effect. A good indication of suitable amounts is given in the Table on pages 7 and 8 hereinafter. Suitable amounts of the copper salt, the amine and ammonium hydroxide can readily be determined by routine experiment but,

in general, are from 5 to 450 grams per litre, especially 50, more particularly 100, to 200grarns per litre.

It has been found that the behaviour of the plating bath can be improved, particularly when the workpiece is of an aluminum alloy, by adding thereto a source of fluoride ions, particularly ammonium and potassium fluorides and bifluorides. Such fluorides may be incorporated in the bath in concentrations of, for example, from 0.1 to l0grams per litre, especially from 0.5 to 2 grams per litre.

The plating bath may also contain other compounds and additivessuch as are commonly used in the art, for example wetting agents and brighteningagents. The incorporation ,of sodium chloride in the bath also has been found to enhance the adhesion of the copper deposit to ,the aluminum .workpiece.

Theternperature forthe bath suitably is within the range of from.,25C. to C. and for the most cases temperature of from 25C. to 30C. can be used. The operating voltage in actual practice may be largely dictated by the work load such as the jigging arrangement (the spacing between anodes and the articles to -be plated) but thegoverning parameter is the current den- Dense, adherent and semi-bright deposits of copper are produced in accordance with the invention in a regular and uniform manner with reproduceable results. The operating conditions of the method need not be subject to any more stringent control than is usual in conventional electroplating processes.

While the alkaline plating bath can bring about sufficient dissolution of the protective oxide layer on the aluminum workpiece it is preferred to subject the workpiece to an initial cleaning or degreasing operation thereby to improve the adhesion of the copper deposit. One suitable cleaning operation comprises treating the workpiece with an aqueous solution of sodium bicarbonate, sodium hydroxide and trisodium phosphate, rinsing with water, etching with nitric acid and again rinsing with water. The aqueous solution may, for

example, comprise about 23 grams per litre of sodium carbonate, about 46 grams per litre of sodium hydroxide and about 23 grams per litre of trisodium phosphate. nitric acid is suitable for use in the etching step and immersion in such acid for a period of up to 3 minutes, for example 10 to seconds, is sufficient. As will be appreciated by those skilled in the art, the cleaning process can be varied substantially within wide limits depending for example on the nature of the workpiece and on the degree and type of surface soiling. After the cleaning operation, when such is carried out, the workpiece is transferred to the plating bath and plated at a suitable current density and temperature in accordance with the method of the invention.

The invention is illustrated by Examples 1 to 9 which are summarised in the Table below. The Table gives details of the plating bath compositions, the conditions under which plating took place and the results and performance of the plating operation. In each case the electroplating was carried out on an aluminum workpiece in a Hull Cell (see Metal Finishing, January 1947, pages 59 to 63). Prior to immersion in the plating bath the workpiece had been cleaned with an aqueous solution containing 23 grams per litre sodium carbonate, 46 grams per litre sodium hydroxide and 23 grams per litre trisodium phosphate, rinsed with water, etched for 10 to 20 seconds with 50% nitric acid, and again rinsed with water.

TABLE-COMPOSlTlONSi oPlRATifid'c'oiTolrloNs & PERFORMANCE OF PLATING BATHS (Hull cell tests) Bath composition Conditions of plating Results Maxi- Current Platmum Cur- Voltdensity ing thick- Temp. rent age Time range range ness Adhe- Example ingredients pH (C) (amp) (volt) (min.) (A/ftfi) ratio (mils.) sion Coppernitrate............ Triethylamine..................... 9.5 25 5 16 2 -250 3.1 0.4 Fair. Ammonium hydroxide (30%). Coppernitrate.................... I 2.... Triethano1amine.................. 9.0 25 5 16 2 115300 2.6 .4 Fair.

Ammonium hydroxide (30%). Coppernitrate.................... 3.. Diethylenetriamlne.... 1S0 gll....... 10.7 25 5 l5 2 10-200 20 .3 Fair.

Ammonium hydroxide 100 mil] (30%). Coppernitrate..... 150g/l....... 4... Tetraethylene 150 g/l....... 10.0 25 1.5 6 S S- l7 .4 Good.

pentamine. Ammonium hydroxide ml/l (30%). Copper nitrate g/l Tetraethylene 150 g/l 5 pentamine. 10.0 25 4 ll 5 10-200 20 .5 Good.

Ammonium nitrate 12 g/l Ammonium hydroxide qs for pH (30%). Copper nitrate 150 g/l... Tetraethylene 150 g/l 6 pentamine. 10.0 25 4 20 5 10-210 21 .5 Good.

Ammonium citrate 50 g/L. Ammonium hydroxide qs for pH (30%). Coppernitrate 150 g/l Tetraethylene 120 g/l 7 pentamine. I00 25 2 1l 2 5-100 20 .3 Good.

Sodiumchloride 50g/l... Ammonium hydroxide qs for pH (30%). Copper nitrate 250 g/l Tetraethylene 250 g/l 8 pentamine. 10.8 25 2 7.0 2 5-100 20 .4 Good.

Ammonium hydroxide ml/l (30%). Copper nitrate 450 g/l Tetraethylene 450 g/l 9 pentamine. 11.6 25 2.0 17.0 2 5-120 24 .4 Good.

Ammonium hydroxide 450 ml/l a. The adhesion of the copper deposit on the workpiece was assessed by the 90 bend test. In this test the workpiece is bent through an angle of 90. Poor and inadequate adhesion is indicated by flaking off of the deposit, while cracking of the deposit is indicative of only a fair adhesion. The absence of flaking or cracking indicates a good, strongly adherent, deposit.

As can be seen from the results in the Table the present invention provides a method of electroplating copper directly onto aluminum and produces strongly adherent deposits. Themethod avoids theneed for involved and costly pretreatments of the aluminum workpiece and it is notnecessary to provide a metal strike layer, for example of zinc, on the aluminum before depositing the copper layer. The plating bath is alkaline and hence is unlike the acidic plating-baths generally used in the plating of copper or aluminum; Because of this the method also avoids the disadvantages associated with the presence of hydrogen at the copper- /aluminum interface. Not only does hydrogenat the interface deleteriously affect the adhesion of the copper deposit but it is usually also necessary totake steps to remove the hydrogen from the plated workpiece after the plating operation. This can involve either leaving the plated workpiece at room temperature for prolonged periods or heating it at a high temperature to facilitate rapid removal of the hydrogen.

This method may be applied to the deposition of copper on aluminum workpieces of virtually any shape, and irregularly shaped workpieces have been satisfactorily plated in accordance with the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of electroplating copper directly onto aluminum without the necessity of providing a pretreatment zinc coating which comprises the steps of a. immersing an aluminum workpiece in an aqueous ammonium hydroxide plating bath having a pH of 8.5. to 13 and which comprises from 5 to 450 grams per liter of a salt of divalent copper and from 5 to 450 grams per liter of a complexing agent selected from the group consisting of primary, secondary and tertiary amines, whereby said complexing agent is capable of forming a complex ion with divalent copper; and

b. passing an electric current through said bath between said workpiece as the cathode and an anode, said electric current being of sufficient density to achieve the desired plating of a layer of copper on aluminum.

2. A method of electroplating copper directly onto aluminum without the necessity of providing a pretreatment zinc coating which comprises the steps of a. immersing an aluminum workpiece in an aqueous plating bath having a pH of 8.5 to 13 consisting essentially of from 5 to 450 grams per liter of ammoniumhydroxide from 5 to 450-grams per liter of the nitrate, sulfate, acetate or chloride salt of divalent copper and from 5 to 450 gramsper li er of a complexing agent selected from the group consistin of primary. secondary and tertiary amines, whereby' said complexing agent-ls capable of forming a complea: ion with divalent copper; and

b. passing an electric current through said bath be= tween saidwarkpiece as the cathode and an anode,

said electric current being of sufiicientdensity to, achieve the desired plating of a layer ofcoppenon aluminum.

3. Method as claimed in claim I, wherein the. plating. bath comprises from 50 to 200 grams per litre .ofthei.

salt of divalent copper and from .50'to200 grams per. litre of the complexing agent. i

4. Method as claimed in claim 1, wherein the plating bath comprises from 100 to 200 grams perlitre of the salt of divalent copper and from 100 to ZOOgrams perv litre of the complexing agent, A

5. Method as claimed in claim 1, wher einthe copper, salt is selected from copper nitrate, copper. sulfate, cop? per acetate and copper chloride.

6. Method as claimed in claim 1, whereirythe amine, contains at least two nitrogenatoms andiscapable of forming a chelate with divalent copper, said. amine being. admixed with ammonium hydroxide of, predcte L- mined concentration to form the complexingagent.

7. Method.- as claimed, in. claim, l 6 wl 1ere in the amine is selected from ethylenediamine, diethylenetriamine. and tetraethylenepentamine and; is admixed monium hydroxide of predetermined; concentration to form the complexing agent. 7

8. Method as claimed in claim 1 wherein. the copper; salt is selected from copper nitrate, copper sulfate, per acetate and copper chloride and the complexing agent is an admixture of ammonium hydroxide with an amine selected from ethylenediamine, diethylenetriamine and tetraethylenepentamine.

9. Method as claimed in claim 1, wherein the plating bath temperature is from 25 to 9QC. I l

10. Method as claimed in claim 12, wherein the plating bath temperature is from 25 to 30C.

11. Method as claimed in claim 1, wherein the oper; ating current density is from it) to 300 amperes per square foot.

12. Method as claimed in claim 1, wherein the operating voltage of the plating bath is from 5 to 25 volts.

13. Method as claimed in claim 1, wherein the aluminum workpiece is degreased before it is immersed into the plating bath. i

14. Method as claimed in claim 13, wherein the aluminum workpiece is degreased before it is immersed into the plating bath by treating with an aqueous solution of sodium bicarbonate, sodium hydroxide and trisodium phosphate, rinsing with water, etching with nitric acid and again rinsing with water.

15. Method as claimed in claim 1, wherein the plating bath also contains a source of fluoride ions. V H v 16. Method as claimed in claim 1 wherein the copper salt is selected from copper nitrate copper sulfate, copper acetate and copper chloride and the complexing agent is an admixture of ammonium hydroxide .with an amine selected from ethylenediamine, t .lie,thylen etriamine and tetraethylenepentarnine, .the electroplating beingcarriedout at current densities between 10 and 300 amperesper square footand at voltages between 5 to25 volts to.achievedesiredplating of copper on aluminum, and the aluminum workpiece ubeingldcgreased before it isirnrnersed into-th plating-bath ,and theplating operationbeing carried out in thepresence of a source of fluorideions which consists of ammonium orpotassium fluorides or bifluorides andispresent lathe bath in concen ions. of. 0.1 to 1.0. gtarnsper litre.

17. Method as claimed in claim 1, in which the plating bath comprises 150 g/l of copper nitrate, 150 g/l of triethylamine'and 100 ml/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 9.5, and the plating is carried out in a current density range of 80 250 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

18. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/l of triethanolamine and 200 m/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 9 and the plating is carried out in a current density range of 115 300 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

19. Method as claimed in claim 1, in which the plating bath comprises 150 g/l of copper nitrate, 150 g/l of diethylenetriamine and 100 ml/l of ammonium hydroxide of 30% concentration and has a pH of about 10.7, and the plating is carried out in a current density range of 10 200 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

20. Method as claimed in claim 1, in which the plating bath comprises 150 g/l of copper nitrate, 150 g/l of tetraethylenepentamine and 100 ml/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 10, and the plating is carried out in a current density range of 85 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

21. Method as claimed in claim I, in which the plating bath comprises 150 g/l of copper nitrate, 150 g/ 1 of tetraethylenepentamine, 12 g/l of ammonium nitrate and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 200 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

22. Method as claimed in claim 1, in which the plating bath comprises 150 g/l of copper nitrate, 150 g/l of tetraethylenepentamine, 50 g/l of ammonium citrate and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 10 210 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

23. Method as claimed in claim 1, in which the plating bath comprises 150 g/l of copper nitrate, 120 g/l of tetraethylenepentamine, 50 g/l of sodium chloride and an amount of ammonium hydroxide of 30% concentration sufiicient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 5 amperes per square foot for a time sufficient to achieve a plating of predetennined thickness.

24. Method as claimed in claim 1, in which the plating bath comprises 250 g/l of copper nitrate, 250 g/l of tetraethylenepentamine and 165 ml/ 1 of ammonium hydroxide of 30% concentration and has a pH of about 10.8, and the plating is carried out in a current density range of 5 100 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

25. Method as claimed in claim 1, in which the plating bath comprises 450 g/l of copper nitrate, 450 g/l of tetraethylenepentamine and 450 m/l of ammonium hydroxide of 30% concentration and has a pH of about 11.6, and the plating is carried out in a current density range of 5 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.

v UNITED STATES PATENT UFFICE CERTIFICATE OF CURREQTWN Patent No. 3 775',265 Dated November 27, 1.973

lnvent fl B'haruoha at al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 27, delete "A" and substitute -a,

Column 1, line 50, after "amine" insert -and-.

Column 5, line 17, delete "or" and substitute on Column 6, line 21, delete "l6" and substitute -6--.

Column 6, line 34, delete "19" and substitute --9--.

Signed and sealed this 5th day of November 19740 (SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-lOSO (10-69) USCOMNPDC 6037mm) t ucsc GOVERNMENT PRINTING OFFICE: I969 o-aee-au. 

2. A method of electroplating copper directly onto aluminum without the necessity of providing a pretreatment zinc coating which comprises the steps of a. immersing an aluminum workpiece in an aqueous plating bath having a pH of 8.5 to 13 consisting essentially of from 5 to 450 grams per liter of ammonium hydroxide from 5 to 450 grams per liter of the nitrate, sulfate, acetate or chloride salt of divalent copper and from 5 to 450 grams per liter of a complexing agent selected from the group consisting of primary, secondary and tertiary amines, whereby said complexing agent is capable of forming a complex ion with divalent copper; and b. passing an electric current through said bath between said workpiece as the cathode and an anode, said electric current being of sufficient density to achieve the desired plating of a layer of copper on aluminum.
 3. Method as claimed in claim 1, wherein the plating bath comprises from 50 to 200 grams per litre of the salt of divalent copper and from 50 to 200 grams per litre of the complexing agent.
 4. Method as claimed in claim 1, wherein the plating bath comprises from 100 to 200 grams per litre of the salt of divalent copper and from 100 to 200 grams per litre of the complexing agent.
 5. Method as claimed in claim 1, wherein the copper salt is selected from copper nitrate, copper sulfate, copper acetate and copper chloride.
 6. Method as claimed in claim 1, wherein the amine contains at least two nitrogen atoms and is capable of forming a chelate with divalent copper, said amine being admixed with ammonium hydroxide of predetermined concentration to form the complexing agent.
 7. Method as claimed in claim 16, wherein the amine is selected from ethylenediamine, diethylenetriamine and tetraethylenepentamine and is admixed with ammonium hydroxide of predetermined concentration to form the complexing agent.
 8. Method as claimed in claim 1, wherein the copper salt is selected from copper nitrate, copper sulfate, copper acetate and copper chloride and the complexing agent is an admixturE of ammonium hydroxide with an amine selected from ethylenediamine, diethylenetriamine and tetraethylenepentamine.
 9. Method as claimed in claim 1, wherein the plating bath temperature is from 25* to 90*C.
 10. Method as claimed in claim 19, wherein the plating bath temperature is from 25* to 30*C.
 11. Method as claimed in claim 1, wherein the operating current density is from 10 to 300 amperes per square foot.
 12. Method as claimed in claim 1, wherein the operating voltage of the plating bath is from 5 to 25 volts.
 13. Method as claimed in claim 1, wherein the aluminum workpiece is degreased before it is immersed into the plating bath.
 14. Method as claimed in claim 13, wherein the aluminum workpiece is degreased before it is immersed into the plating bath by treating with an aqueous solution of sodium bicarbonate, sodium hydroxide and trisodium phosphate, rinsing with water, etching with nitric acid and again rinsing with water.
 15. Method as claimed in claim 1, wherein the plating bath also contains a source of fluoride ions.
 16. Method as claimed in claim 1, wherein the copper salt is selected from copper nitrate, copper sulfate, copper acetate and copper chloride and the complexing agent is an admixture of ammonium hydroxide with an amine selected from ethylenediamine, diethylenetriamine and tetraethylenepentamine, the electroplating being carried out at current densities between 10 and 300 amperes per square foot and at voltages between 5 to 25 volts to achieve desired plating of copper on aluminum, and the aluminum workpiece being degreased before it is immersed into the plating bath, and the plating operation being carried out in the presence of a source of fluoride ions which consists of ammonium or potassium fluorides or bifluorides and is present in the bath in concentrations of 0.1 to 10 grams per litre.
 17. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/1 of triethylamine and 100 ml/1 of ammonium hydroxide of 30% concentration and has a pH of about 9.5, and the plating is carried out in a current density range of 80 - 250 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 18. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/1 of triethanolamine and 200 m/1 of ammonium hydroxide of 30% concentration and has a pH of about 9 and the plating is carried out in a current density range of 115 - 300 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 19. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/1 of diethylenetriamine and 100 ml/1 of ammonium hydroxide of 30% concentration and has a pH of about 10.7, and the plating is carried out in a current density range of 10 - 200 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 20. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/1 of tetraethylenepentamine and 100 ml/1 of ammonium hydroxide of 30% concentration and has a pH of about 10, and the plating is carried out in a current density range of 5 - 85 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 21. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/1 of tetraethylenepentamine, 12 g/1 of ammonium nitrate and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the platIng is carried out in a current density range of 10 - 200 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 22. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 150 g/1 of tetraethylenepentamine, 50 g/1 of ammonium citrate and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 10 - 210 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 23. Method as claimed in claim 1, in which the plating bath comprises 150 g/1 of copper nitrate, 120 g/1 of tetraethylenepentamine, 50 g/1 of sodium chloride and an amount of ammonium hydroxide of 30% concentration sufficient to make the bath of a pH of about 10, and the plating is carried out in a current density range of 5 - 100 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 24. Method as claimed in claim 1, in which the plating bath comprises 250 g/1 of copper nitrate, 250 g/1 of tetraethylenepentamine and 165 ml/1 of ammonium hydroxide of 30% concentration and has a pH of about 10.8, and the plating is carried out in a current density range of 5 - 100 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness.
 25. Method as claimed in claim 1, in which the plating bath comprises 450 g/1 of copper nitrate, 450 g/1 of tetraethylenepentamine and 450 m/1 of ammonium hydroxide of 30% concentration and has a pH of about 11.6, and the plating is carried out in a current density range of 5 - 120 amperes per square foot for a time sufficient to achieve a plating of predetermined thickness. 